Radio-frequency identification (RFId) is an automatic identification method, relying on storing and remotely retrieving data using devices called RFId tags or transponders. The technology requires some extent of cooperation of an RFId reader and an RFId tag. The reading reliability of an RFId system depends mainly on the proper exposure of the RFId tag to the electromagnetic field radiated by the antenna reader. Once the transponder is exposed to the electromagnetic filed radiated by the reader, it collects the necessary power for activation and for sending a response signal to the reader. However in the case of high tag density or when tags are used with non-compliant RFId materials (e.g. liquid, metal) or when they are applied on goods that can not be moved, it is difficult to properly expose the transponder to the radiated electromagnetic field and identify it with standard RFId antenna system.
Reconfigurable RFid antenna networks have been proposed that use a switch matrix including a single pole multiple throw switch, a plurality of reconfigurable antennae, and a controller for controlling the state of the switch matrix. For example, U.S. Pat. No. 7,319,398 discloses such a system where a reader unit uses different antennae located at multiple points within and on shelves for reading RFid tags of items on the shelves.
In other RFid tag reading systems, such as that described in U.S. Pat. No. 7,496,329, a scanning reconfigurable antenna system having phased arrays of variable capacitors or parasitic elements or variable dielectrics is used to scan the RFid tags.
However, such prior art systems are limited in that they do not permit the shape and polarization of the electromagnetic field to be changed so as to concentrate the electromagnetic field towards the transponder to more effectively and efficiently read RFid tags that may otherwise be difficult to read. Moreover, such prior art systems do not allow for efficient power transfer, thereby limiting the range of the antenna systems. The present invention is designed to address these and other needs in the art.